Trace concentrations of iron nanoparticles cause overproduction of biomass and lipids during cultivation of cyanobacteria and microalgae

Cultivation in Zehnder medium containing 5.1 mg L-1 zero-valent iron nanoparticles (nZVI) boosted the growth of the green algae Desmodesmus subspicatus, Dunaliella salina, Parachlorella kessleri and Raphidocelis subcapitata and the eustigmatophycean algae Nannochloropsis limnetica and Trachydiscus minutus. In the cyanobacterium Arthrospira maxima, growth stimulation occurred at 1.7-5.1 mg L-1 nZVI. In all studied microorganisms, 5.1 mg L-1 nZVI strongly enhanced lipid accumulation, decreased the content of saturated and monounsaturated fatty acids with the exception of palmitoleic acid and increased the content of polyunsaturated fatty acids in cells. The nZVI particles may provide a suitable source of iron causing increased cell growth and induce metabolic changes resulting in higher lipid production and changes in fatty acid (FA) composition. Altered lipid synthesis may reflect the oxidative action of nZVI. Further research may contribute to optimizing the economical production of oils from oleaginous microorganisms and help clarify the mechanism of nZVI action.